The present invention relates to deformable membrane assemblies in which fluid pressure is used to control the shape of an elastic membrane by applying a fluid directly to one face of the membrane, and has particular reference to fluid-filled lenses and mirrors in which the elastic membrane forms a lens or mirror surface, and the pressure of the fluid is controlled to adjust the degree of curvature of the membrane and thus the power of the lens or mirror. The invention is equally applicable to other apparatus or equipment, such as acoustic transducers and the like, in which an elastic surface of statically or dynamically variable shape is required.
Fluid filled lenses of the kind in which the pressure of fluid is used to control the shape of an elastic membrane in contact with the fluid are known in the art. Generally these lenses may be of the “fluid injection” type, in which the amount of fluid is controlled within an envelope having a substantially fixed volume that is bounded on one side by the membrane, or the “fluid compression” type in which the volume of an envelope is adjusted that is bounded on one side by the membrane and contains a fixed amount of fluid. In each case, the pressure of the fluid within the envelope is adjusted, either by adding or removing fluid to or from the envelope, or by changing the volume of the envelope, to control the fluid pressure acting on the membrane, thereby to control the shape of the membrane.
Whilst various applications of adjustable lenses are possible, for example in cameras and other optical equipment, one use is in eyewear. An adjustable lens is particularly useful for correction of presbyopia—a condition in which the eye exhibits a progressively diminished ability to focus on close objects with age. An adjustable lens is advantageous because the wearer can obtain correct vision through a range of distances from long-distance to near vision. This is more ergonomic than bifocal lenses in which near-vision correction is provided in a bottom region of the lens, thereby only allowing the user to see close objects in focus when looking downwardly.